net.sf.saxon.expr.sort

Class GroupByIterator

java.lang.Object

net.sf.saxon.expr.sort.GroupByIterator

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, LastPositionFinder, GroupIterator, SequenceIterator<Item<?>>, LookaheadIterator<Item<?>>

public class GroupByIterator
extends java.lang.Object
implements GroupIterator, LastPositionFinder, LookaheadIterator<Item<?>>

A GroupByIterator iterates over a sequence of groups defined by xsl:for-each-group group-by="x". The groups are returned in order of first appearance. Note that an item can appear in several groups; indeed, an item may be the leading item of more than one group, which means that knowing the leading item is not enough to know the current group.

The GroupByIterator acts as a SequenceIterator, where successive calls of next() return the leading item of each group in turn. The current item of the iterator is therefore the leading item of the current group. To get access to all the members of the current group, the method iterateCurrentGroup() is used; this underpins the current-group() function in XSLT. The grouping key for the current group is available via the getCurrentGroupingKey() method.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	GroupByIterator.ManualGroupByIterator

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	composite
protected java.util.List<AtomicSequence>	groupKeys
protected java.util.List<java.util.List<Item<?>>>	groups
protected Expression	keyExpression

Fields inherited from interface net.sf.saxon.om.SequenceIterator

ATOMIZING, GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

Constructors

Constructor and Description
GroupByIterator()
GroupByIterator(SequenceIterator<?> population, Expression keyExpression, XPathContext keyContext, StringCollator collator, boolean composite) Create a GroupByIterator

Method Summary

Modifier and Type	Method and Description
void	close() Close the iterator.
java.util.List	getCurrentGroup() Get the contents of the current group as a java List
AtomicSequence	getCurrentGroupingKey() Get the value of the grouping key for the current group
int	getLength() Get the last position (that is, the number of groups)
int	getProperties() Get properties of this iterator, as a bit-significant integer.
ManualGroupIterator	getSnapShot(XPathContext context) Get a sequence which is a snapshot of this sequence at the current position
boolean	hasNext() Determine whether there are more items to come.
SequenceIterator<?>	iterateCurrentGroup() Get an iterator over the items in the current group
Item	next() Get the next item in the sequence.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface net.sf.saxon.om.SequenceIterator

forEachOrFail, materialize

Field Detail

keyExpression

protected Expression keyExpression

groups

protected java.util.List<java.util.List<Item<?>>> groups

groupKeys

protected java.util.List<AtomicSequence> groupKeys

composite

protected boolean composite

Constructor Detail

GroupByIterator

public GroupByIterator(SequenceIterator<?> population,
                       Expression keyExpression,
                       XPathContext keyContext,
                       StringCollator collator,
                       boolean composite)
                throws XPathException

Create a GroupByIterator

Parameters:

population - iterator over the population to be grouped

keyExpression - the expression used to calculate the grouping key

keyContext - dynamic context for calculating the grouping key

collator - Collation to be used for comparing grouping keys

composite - true if grouping keys are to be treated as composite keys

Throws:

XPathException - if an error occurs

GroupByIterator

public GroupByIterator()

Method Detail

getCurrentGroupingKey

public AtomicSequence getCurrentGroupingKey()

Get the value of the grouping key for the current group

Specified by:

getCurrentGroupingKey in interface GroupIterator

Returns:

the grouping key

iterateCurrentGroup

public SequenceIterator<?> iterateCurrentGroup()

Get an iterator over the items in the current group

Specified by:

iterateCurrentGroup in interface GroupIterator

Returns:

the iterator

getCurrentGroup

public java.util.List getCurrentGroup()

Get the contents of the current group as a java List

Returns:

the contents of the current group

hasNext

public boolean hasNext()

Description copied from interface: LookaheadIterator

Determine whether there are more items to come. Note that this operation is stateless and it is not necessary (or usual) to call it before calling next(). It is used only when there is an explicit need to tell if we are at the last element.

This method must not be called unless the result of getProperties() on the iterator includes the bit setting SequenceIterator.LOOKAHEAD

Specified by:

hasNext in interface LookaheadIterator<Item<?>>

Returns:

true if there are more items in the sequence

next

public Item next()
          throws XPathException

Description copied from interface: SequenceIterator

Get the next item in the sequence. This method changes the state of the iterator.

Specified by:

next in interface SequenceIterator<Item<?>>

Returns:

the next item, or null if there are no more items. Once a call on next() has returned null, no further calls should be made. The preferred action for an iterator if subsequent calls on next() are made is to return null again, and all implementations within Saxon follow this rule.

Throws:

XPathException - if an error occurs retrieving the next item

close

public void close()

Description copied from interface: SequenceIterator

Close the iterator. This indicates to the supplier of the data that the client does not require any more items to be delivered by the iterator. This may enable the supplier to release resources. After calling close(), no further calls on the iterator should be made; if further calls are made, the effect of such calls is undefined.

For example, the iterator returned by the unparsed-text-lines() function has a close() method that causes the underlying input stream to be closed, whether or not the file has been read to completion.

Closing an iterator is important when the data is being "pushed" in another thread. Closing the iterator terminates that thread and means that it needs to do no additional work. Indeed, failing to close the iterator may cause the push thread to hang waiting for the buffer to be emptied.

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface SequenceIterator<Item<?>>

getProperties

public int getProperties()

Get properties of this iterator, as a bit-significant integer.

Specified by:

getProperties in interface SequenceIterator<Item<?>>

Returns:

the properties of this iterator. This will be some combination of properties such as SequenceIterator.GROUNDED, SequenceIterator.LAST_POSITION_FINDER, and SequenceIterator.LOOKAHEAD. It is always acceptable to return the value zero, indicating that there are no known special properties. It is acceptable for the properties of the iterator to change depending on its state.

getLength

public int getLength()
              throws XPathException

Get the last position (that is, the number of groups)

Specified by:

getLength in interface LastPositionFinder

Returns:

the number of items in the sequence

Throws:

XPathException - if an error occurs evaluating the sequence in order to determine the number of items

getSnapShot

public ManualGroupIterator getSnapShot(XPathContext context)

Description copied from interface: GroupIterator

Get a sequence which is a snapshot of this sequence at the current position

Specified by:

getSnapShot in interface GroupIterator